Aqueousslurry type nitrocarbonitrate blasting compositions containing flake aluminum-dinitro-toluene as the only sensitizer



United States Patent John D. Ferguson, Wilmington, Del., assignor to Hercules Incorporated, a corporation of Delaware No Drawing. Filed July 20, 1965, Ser. No. 473,483 9 Claims. (Cl. 149-39) This invention relates to aqueous inorganic oxidizer salt type slurry blasting compositions of the nitrocarbonitrate type containing a novel combination of aluminum and dinitrotoluene as the sensitizer component.

Inorganic oxidizer salt blasting compositions of the aqueous slurry type have had wide use in the explosives industry in recent years. However, it has been necessary that these compositions, in order to be detonatable by a conventional booster charge, contain smokeless powder or a high explosive such as TNT, PETN or the like as the sensitizer except that in a number of instances, large amounts of finely divided metals such as particulate aluminum have been utilized for that purpose. The use of smokeless powder and high explosives in these slurry compositions has been disadvantageous particularly from the standpoint of manufacturing hazards involving handling of these highly sensitive materials, and the use of large amounts of finely divided metals has been economically unfeasible.

This invention is concerned with oxidizer salt blasting compositions of the aqueous slurry type which contain finely divided aluminum in small proportions and are devoid of smokeless powder and high explosive sensitizer components but which, nevertheless, are detonatable by conventional booster systems.

In accordance with the invention, aqueous inorganic oxidizer salt slurry type explosives are provided which contain, on a weight basis, a combination of from about 3 to 20 percent flaked aluminum with from about 2 to 15 percent dinitrotoluene (DNT), as the sensitizer component. The slurry compositions generally contain from about 8 to 25 percent water, from about 30 to 75 percent of an inorganic oxidizer salt, the above described sensitizer component and from about 0.2 to percent of a thickener.

In a now preferred practice of the invention, the oxidizer salt component is either ammonium nitrate alone or together with sodium nitrate in a weight ratio to the sodium nitrate as low as about 0.5:1, generally within the range of from about 2:1 to 4:1, and the thickener is guar gum in crosslinked (or gelled) form. In preferred practice, the compositions of the invention contain (weight basis) from 12 to 20 percent water, from 40 to 70 percent ammonium nitrate, more preferably 40 to 60 percent, from 5 to 30 percent sodium nitrate, more preferably to 20 percent, from 5 to percent flaked aluminum, from 0.2 to 2 percent guar gum, more preferably up to 1.5 percent when in crosslinked form, and 4 to 12 percent DNT.

By the term inorganic oxidizer salt, as is well known in the explosives art, is meant one which under the conditions of the detonation, liberates oxygen for the oxygen balance required.

The ammonium nitrate is in many instances the only inorganic oxidizer salt component. However, other inorganic oxidizer salts can be used, alone or with ammonium nitrate as a supplementary oxidizer salt. Of these "ice supplementary salts, the alkali metal nitrates are now preferred. Often when ammonium nitrate is utilized with a supplementary salt, it comprises a major proportion of the tot-a1 oxidizer salt, i.e., at least 50 percent of the total oxidizer salt. Exemplary inorganic oxidizer salts that can be used alone, or together with ammonium nitrate, are alkali metal and alkaline earth metal nitrates and perchlorates (including ammonium) as for'example, sodium nitrate, magnesium nitrate, calcium nitrate, potassium nitrate, barium nitrate, sodium perchlorate, ammonium perchlorate, calcium perchlorate and magnesium perchlorate.

Particle size and type of the oxidizer salt ingredient are not generally critical. For example, ammonium nitrate can consist of prills such as used in fertilizers and which are substantially all on 20 mesh, or it can be granular and in that form, vary from coarse to fine. Other oxidizer salt ingredients are generally of comparable particle size.

The DNT component can be an oil, a solid, or an oilsolid mixture. As an oil, the DNT component is a mixture of DNT isomers and often has a freezing point in the range of about 20-35 C., and as a solid, it is essentially 2,4-dinitrotoluene.

The flakes of the aluminum component generally have a thickness less than 0.002" and a diameter (or maximum cross-sectional dimension) in the range of from somewhat less than 0.0098 to 0.0232", chopped aluminum foil being particularly well suited.

The thickener content can be as high as 5 percent dependent upon the particular thickener and the desired consistency of the finished composition. Generally, a thickener content up to about 2 percent is sufficient. When the thickener content is within the range of 0.2 to 0.5 weight percent, there is suflicient thickening to prevent settling of the composition ingredients, although additional thickener is often required in order to impart a satisfactory degree of cohesiveness so that the composition retains its form as a unit mass, preferably plastic but deformable. Exemplary thickeners are sodium carboxymethylcellulose, Kara'ya gum, water soluble starches, locust bean gum, cereal products and the like. When the thickener is guar gum in crosslinked form, in accordance with preferred practice, the guar content is most advantageously within the range of from 0.5 to 1.5 percent, under which conditions the finished composition is a plastic, rubbery, but deformable, mass.

The compositions of the invention are in most instances insensitve to detonating action of a No. 8 commercial blasting cap but are, in all events, detonatable by conventional booster charges of PETN (pentaerythritol tet-ranitrate), RDX (cyclotrimethylenetrinitramine), Pentolite (PETN-TNT, 50/50), tetryl, Composition B (RDX- TNT, 60/40) and the like. One booster advantageously employed is a dispersion of a crystalline high explosive, e.g., PETN or RDX in a plastic carrier such as described in the copending application of Alpheus M. Ball, Ser. No. 538,788, filed Oct. 5, 1955, and which is detonated by either a commercialblasting cap or a detonating fuse. in general, these compositions are detonatable in response to any secondary explosive.

The explosive compositions of the invention are of the well known class of nitrocarbonitrates, by which term it is meant there are no sensitizers which in themselves are high explosives, and the mixtures will not detonate with a No. 8 blasting cap when packed for shipment.

The invention is illustrated with reference to the following formulations, all on a weight percent basis.

TABLE 1 Water 1 Dinitrotoluene Barium Nitrate L Ammonium Nitrate 50. Sodium Nitrate 19 Calcium Nitrate Aluminum Flakes Detonation Rate (m./see.,

5 x 28 pipe) Detonator, gr2 17ns: 7

20 Funnel Test: 5 Flow Time, sec.-.

Would still flow slowly through a large (4" diameter) funnel.

Solid 2,4-dinitrotoluene.

2 Substantially all through 40-mesh screen and substantially all on IOU-mesh screen.

3 Granular, varying from Fine to Coarse.

4 In crosslinked form.

6 Flaked aluminum (chopped foil) 99 percent. through 10 mesh, 50 percent through 20 mesh, 20 percent through 40 mesh.

Measured as average detonation velocity over a 20 cm. length, at the end of a 28 long column of explosive. The explosive is confined 1D 5" Runs 1-11 illustrate various proportions of components of the compositions of the invention.

The invention is further illustrated with reference to the tabulation of Table 2, which demonstrates the role of aluminum in flake form.

TABLE 2 Water 16. 0 1e. 0 16.0 1e. 0 Dinitrotoluene 8. 0 8. 0 8. 0 8. 0 Ammonium Nitrate 48. 5 48. 5 48. 5 48. 5 Sodium Nitrate 15. 0 15. 0 15.0 15.0 Guar Gum 4 1. 0 1. 0 1.0 1.0 Aluminum Flakes 0.

Aluminum Granules Do 7 Do 5 I Ethylene Glycol... .5 Density, gJcc .49 1. 49 1. 47 Detonation Rate (rm/sec.)

5 x 28" pipe) Detonator, gra$sz Failure 1 Liquid 2,4-dintrotoluene freezing point 35C. 2 See footnote 2 of Table 1. 3 See footnote 3 of Table 1. See footnote 4 of Table 1. 5 See footnote 5 of Table 1. 6 Substantially all through 12 mesh, on 40 mesh. 7 Substantially all through 200 mesh. 8 Substantially all through 400 mesh. 9 See footnote 6 of Table 1.

See footnote 7 of Table l.

diameter (nominal) balok iron pipe (Schedule 40). The time for detonation to proceed across the 20 cm. length of explosive is measured electronically with a counter-chronograph. Run Nos. 9, 10 and 11, estimated.

t20 gram charge is PETN in copper shell; all other, 50/50 Pentolite, cas

Approximately 5000 grams of slurry is poured into an aluminum funnel having a 1% diameter x 1 orifice. When the orifice is opened to permit flow, the tuning is begun. When light is visible through the orifice (looking down into the funnel), timing is stopped. The time difierenco is designated as the flow time.

TABLE 3 Water 12. 0 l6. 0 12. 0 12. 0 16. 0 16. 0 Dinitrotoluene 4. 0 8. 0 10. 0 8. 0 5. 0 5.0 Ammonium Nitrate 54.0 49. 9 48. 0 55.0 55. 5 58.0 Sodium Nitrate c 19.4 15.0 19. 4 19.4 15. 0 15.0 Guar Gum 4 0. 6 1.0 0. 6 0. 6 1. 0 1.0 Aluminum Flakes 10. 0 10. 0 10. 0 5. 0 7. 5 5. 0 Density, g./cc 1. 43 1. 40 1. 42 1. 41 1. 42 1. 44

Detonation Rate 5 x 28 pipe) Detonator. grams: 7

Failed.

(For footnotes 1 through 7, see corresponding footnotes of Table 1.)

Runs 16, 17 and 18 demonstrate the effect of varying amounts of DNT as sensitizer in combination with a fixed amount of flake aluminum in compositions of the invention. Thus, with 10' percent aluminum, the composition No. 16 was sensitive to detonating action of a gram booster charge but failed in response to action of a 40 gram charge. However, as shown at Run 18, with 10 percent DNT present, the charge was responsive to detonation by a 40gram charge, and the detonation rate was greater. The results of Run 17 demonstrate the role of an intermediate proportion of DNT, i.e., 8.0 percent, which provides increased sensitivity and detonation rate (over composition 16), both, nevertheless, smaller than that of Run 18 containing a slightly'larger proportion of DNT sensitizer.

A comparison of Runs 19 and 21 demonstrates the effect of increase in proportion of the DNT sensitizer utilized in connection with only 5 percent aluminum. Thus, in Run 19, i.e., 8 percent DNT, the charge was sensitive to detonation by a 160 gram detonator charge, whereas even at 500 grams of detonator charge, the charge of Run 21 was insensitive. The data, particularly Runs 19 and 21, demonstrate the small proportions of aluminum that can be utilized in conjunction with DNT, i.e., as low as 5 percent aluminum, but generally requiring at least 8 percent DNT.

In accordance with a now preferred process for the manufacture of slurry compositions of the invention, natural guar gum constituting a minor proportion of the total guar .gum contemplated is added with agitation to the water component together with ammonium nitrate and sodium nitrate and DNT components, the latter as a solid. Under these conditions hydration of the natural guar gum takes place immediately. The resulting admixture is maintained at a temperature in the order of say, 80-100 F. for a period of from 5-10 minutes and is characterized by a sufliciently high viscosity to prevent settling of the ingredients. The aluminum and the remaining portion of the guar gum to be added, the latter in inhibited form, i.e., containing an agent causing a delay in hydration that would otherwise take place immediately, are added to the admixture. The delay, or inhibition, postpones hydration of the last added guar gum so as to permit time for packaging the final product mixture while still easily flowable, with final hydration and subsequent .gelation taking place during storage of the packaged composition.

Various agents contained in the guar gum, and associated conditions for providing the inhibiting and gelation actions above described, are well known. Exemplary agents functioning to inhibit and subsequently promote crosslinking are those which liberate borate, cuprous, calcium and aluminum ions, the inhibiting and gelation reactions being promoted under ditferent pH conditions. For example, sodium borate is commonly utilized as an ingredient of the guar gum at a pH of from about 5-6 to promote inhibition of hydration and promotes crosslinking when the pH is increased to about 7.

In carrying out the process embodiment above described, and utilizing only a minor proportion of the guar gum ingredient in natural form, all guar gum is ultimately crosslinked to provide a rubbery, plastic but deformable mass. Somewhat less than complete crosslinking of the guar gum can be obtained when the natural guar gum is added in a proportion greater than that in inhibited form. Hydration with substantially no gelation can be obtained when only natural guar gum is added, and particularly at a pH below about 7. In all instances, there is a thickening action whether it be the result of hydration alone or with some gelation, or substantially complete gelation.

When referring herein to hydration, it is meant the reaction that takes place between the guar gum and water components to form a sol, and when referring to gelation, or crosslinking, it is meant the crosslinking reaction that takes place between the guar gum and the particular crosslinking agent therein to form a gel.

If the DNT component is an oil, it is generally advantageous to admix about one-half of the contemplated amount of oxidizer salt ingredients with the DNT oil, to permit coating of the DNT on the salt particle surfaces. Thereafter, all remaining ingredients, including the remaining total oxidizer salt, can be added in any desired sequence.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What I claim and desire to protect by Letters Patent is:

1. In a nitrocarbonitrate inorganic oxidizer salt explosive of the aqueous slurry type, the improvement comprising, on a weight basis, from 3 to 20 percent flaked aluminum in combination with from 2 to 15 percent dinitrotoluene, as the only sensitizer component.

2. As an improved aqueous slurry type nitrocarbonitrate blasting composition, on a weight basis, from 8 to 25 percent water, 30 to 75 percent of an inorganic oxidizer salt, from 3 to 20 percent flaked aluminum, from 0.2 to 5 percent of a thickener, and from 2 to 15 percent dinitrotoluene.

3. A composition of claim 2 wherein said thickener is guar gum in crosslinked form present in an amount of from 0.5 to 1.5 percent.

4. A composition of claim 3 containing ammonium nitrate as the only oxidizer salt.

5. A composition of claim 3 containing from 12 to 20 percent water, from 40 to 70 percent ammonium nitrate and from 5 to 30 percent sodium nitrate as said oxidizer salt, from 5 to 15 percent flaked aluminum, up to 2 percent guar gum as said thickening agent, and from 4 to 12 percent dinitrotoluene.

6. A composition of claim 3 wherein said DNT is a solid.

7. A composition of claim 3 wherein said DNT is an oil.

8. A composition of claim 3 wherein said DNT is a solid-oil mixture.

9. A composition of claim 5 containing from 40 to percent of said ammonium nitrate and from 10 to 20 percent of said sodium nitrate.

References Cited UNITED STATES PATENTS 2,136,205 11/1938 Byers 14938 X 2,589,532 3/1952 Byers 149-38 X 2,647,047 7/1953 Richardson 14939 X 3,147,163 9/1964 Griffith et al. 149-55 X 3,166,451 1/1965 Young 14939 3,201,291 8/1965 Schmidt 14956 X 3,216,872 11/1965 Wells 14957 X 2,836,484 5/1958 Strong et al. 149l14 X 3,238,074 3/1966 Grifiith et al. 14939 X L. DEWAYNE RUTLEDGE, Primary Examiner.

BENJAMIN R. PADGETT, CARL D. QUARFORTH, Examiners.

S. J. LECHERT, JR., Assistant Examiner. 

1. IN A NITROCARBONITRATE INORGANIC OXIDIZER SALT EXPLOSIVE OF THE AQUEOUS SLURRY TYPE, THE IMPROVEMENT COMPRISING, ON A WEIGHT BASIS, FROM 3 TO 20 PERCENT FLAKED ALUMINUM IN COMBINATION WITH FROM 2 TO 15 PERCENT DINITROTOLUENE, AS THE ONLY SENSITIZER COMPONENT. 